The present invention broadly relates to vacuum evaporators or vaporizers and, more specifically, pertains to a new and improved construction of an overcharge prevention arrangement for monitoring the level of a fluid surface in a vacuum evaporator of a solvent processing plant having a vacuum pump, a condenser combined with said vacuum evaporator to define a heat exchanger, a feed valve, a condensate trap, a condensate drain, a drain valve and a system of interconnecting conduits.
In solvent processing plants, solvents are reclaimed or recuperated from cleaning fluids or solutions contaminated by fats, dyes or resins by evaporation processes. In such plants, among other things, overload or overcharge, i.e. overfill, prevention devices in the form of capacitive sensors are known which, together with associated electronic circuitry and a feed valve, regulate the level of the fluid charge in the vacuum evaporator. The cleaning solution is drawn through a supply or delivery conduit into the vaporizing space by a vacuum prevailing in the vacuum evaporator. The solvent is evaporated or vaporized out of the cleaning fluid or solution at low temperature. The vapors are compressed to more positive values of pressure by the vacuum pump and delivered to the condensation space of the heat exchanger where they condense or precipitate on the wall surfaces. The condensate drains continuously and unpressurized and is recycled as fully reclaimed solvent. The residue collecting in the lower portion of the vacuum evaporator during operation is periodically drained through a drain valve, usually in a viscous state, and delivered to a waste collecting means. The previously mentioned capacitive sensor is installed in the evaporating or vaporizing space or chamber of the heat exchanger and monitors the level of the surface of the cleaning fluid or solution. If the fluid surface reaches the prescribed upper or maximum level, the sensor responds, the feed valve is closed and the delivery of further cleaning solution is inhibited. The disadvantages of this device are that the electronic sensor elements do not respond to all media and that additional costly protective measures must be taken for explosion-proof designs.
Non-electronic, float-controlled feed valves are known in which a spherical float body monitors the level of the fluid surface and regulates the delivery of cleaning solution. The disadvantage of this overcharge prevention device is that the cleaning solution flowing through the feed valve can influence the functionality of the feed valve. In the course of time, contamination can accrete in the interior of the feed valve and hinder or prevent perfect closure of the feed valve.